Vitamin D plays an important role in bones, muscles, immunity, and calcium regulation.
Vitamin D toxicity is unusual from food or sunlight. When it occurs, it is usually the result of taking **very large amounts of vitamin D supplements for an extended period**.
Excessive vitamin D can cause dangerously high calcium levels.
Possible symptoms include:
* nausea
* vomiting
* weakness
* confusion
* excessive thirst
* frequent urination
* dehydration
Very high vitamin D levels may lead to **kidney stones and, in severe cases, kidney failure**.
People taking high-dose vitamin D for a documented deficiency should follow the dose and monitoring plan recommended by their healthcare professional.
## 3. Vitamin C
Vitamin C is water-soluble, so excess amounts are largely eliminated through urine.
That does not mean extremely high doses are harmless.
Large supplemental doses may increase the amount of oxalate in the urine. In susceptible people, this can contribute to the formation of **calcium oxalate kidney stones**.
People who already have:
* kidney disease
* a history of kidney stones
* disorders that increase oxalate absorption
should be particularly cautious with high-dose vitamin C supplements.
Getting vitamin C from ordinary foods such as citrus fruits, berries, peppers, and vegetables is generally not the concern. The issue is primarily concentrated supplements taken in much larger amounts than the body requires.
## 4. Niacin — Vitamin B3
